Oh, now you're risking a lengthy off-topic digression on the semiotics of technical terms as metaphors! That's a deceptively challenging little snippet of text there (I should probably expect no less from Luhmann!). Maybe:

Zettelkasten as settling pond — not just for fully digested notes. Put off examining and deciding — and keep moving! (Zettel 9/8a2)

(Another digression — I think it makes sense to keep 'zettel' in English to refer to the specific concept/object within the Zettelkasten system while leaving 'note' as a more generic expression.)

It's not a literal translation (obviously)! I took the entire quote as a recommendation or advice to someone who might want to emulate his zettelkasten process (or maybe just to himself; I don't know the context, but unless I'm wrong about his intention it doesn't really matter). I understand "eine Tempofrage" as "a matter of speed" or "(keeping up the) pace", i.e. getting the information into zettel form quickly. He's giving the reader permission to put off examining and deciding and to include not-fully-digested notes in part ("und") for the sake of not allowing the process to bog down. If he's concerned about Tempo and he's acknowledging that these notes are nicht abgeklärt, that strongly suggests that he wants to move on to the next note or to some other task rather than spending time now to complete the Abklärung. Since the style of the German is informal, e.g. it's not written in complete sentences, "keep moving" seemed like the most natural way to express that in English. There's no one word in English that quite corresponds to this sense of Tempo.

FWIW, if this were for publication I'd also want to take a closer look at just what he meant by "abgeklärt".

Mh. I think the main issue here is that we have a different approach on translating. I try to be as close to the phrases as I can get while you are willing to interpret in order to get the point across you see. That is also the reason why I refuse to use "Zettel" and just say (or write) notes. I am very hesitant to touch language.

"Abgeklärt" by the way seems to be a play of words. It has meaning in the context of the settling pond (which is the better translation imho than mine) and meaning in the context of evaluation. Water is "abgeklärt" when the particles settled on the ground. If you are "abgeklärt" you have your shit together (sometimes meant in a slightly derogatory way). German has its strange way with its pre- and suffixes. You can even have an "abgeklärt" deal. You can find [100 synonyms in 4 categories|(https://synonyme.woxikon.de/synonyme/abklären.php) for this word. Our language is quite strange.

I stick closer to the original wording for things like legal documents, but this wasn't that. More broadly, though, my philosophy is that translating is "impossible" anyway — any word or phrase in one language will never mean "exactly" the same thing to a reader in a different language because meaning is always dependent on context, and a different language environment is always a different context. The best you can do is produce a target document that functions as intended in the target language environment. So producing an effective translation is always and irreducibly a matter of subjective judgment. "Traduttore, traditore."